In integrated circuit (IC) manufacturing, a semiconductor die is provided with terminals, commonly referred to as pads, for communicating with a user or other circuits in an application. The die may be housed in a package having user accessible terminals for mounting on a substrate or a printed circuit board. Various methods are used to couple the die pads to the terminals of the package, such as for example, wirebonds or solder balls. Frequently, complex integrated circuit designs incorporate more functions on a single integrated circuit die than can easily be coupled to the user accessible terminals, or pins, on the integrated circuit package housing the die. In some cases, the various signals on the integrated circuit die can be multiplexed to the user accessible terminals using simple digital multiplexers. However, many ICs today include digital circuits requiring more than one supply voltage. For example, a digital signal from one part of the IC may be from a circuit operating from one supply voltage level (for example 1.0 volt), and a digital signal from another part of the IC may be from a circuit operating at another supply voltage level (for example 1.6 volts). Because of the difference in supply voltage levels, a simple digital multiplexer may not be able to reliably multiplex these signals.
Therefore, there is a need for a multiplexing circuit in an IC that can multiplex digital signals that are provided at different supply voltage levels.